[linux-3.10.17] Could not allocate memory from free CMA areas

[PINTU KUMAR]

Hi,

We are facing one problem on linux 3.10 when we try to use CMA as large as 56MB for 256MB RAM device.
We found that after certain point of time (during boot), min watermark check is failing when "free_pages" and "free_cma_pages" are almost equal and falls below the min level.

system details:
ARM embedded device: RAM: 256MB
Kernel version: 3.10.17
Fixed Reserved memory: ~40MB
Available memory: 217MB
CMA reserved 1 : 56MB
ZRAM configured: 128MB or 64MB
min_free_kbytes: 1625 (default)
Memory controller group enabled (MEMCG)


After boot-up the "free -tm" command shows free memory as: ~50MB
CMA is used for all UI display purposes. CMA used during bootup is close to ~6MB.
Thus most of the free memory is in the form of CMA free memory.
ZRAM getting uses was around ~5MB.


During boot-up itself we observe that the following conditions are met.


if (free_pages - free_cma <= min + lowmem_reserve) {
    printk"[PINTU]: __zone_watermark_ok: failed !\n");

    return false;
}
Here: free_pages was: 12940, free_cma was: 12380, min: 566, lowmem: 0


Thus is condition is met most of the time.
And because of this watermark failure, Kswapd is waking up frequently.
The /proc/pagetypeinfo reports that most of the higher order pages are from CMA regions.


We also observed that ZRAM is trying to allocate memory from CMA region and failing.

We also tried by decreasing the CMA region to 20MB. With this the watermark failure is not happening in boot time. But if we launch more than 3 apps {Browser, music-player etc}, again the watermark started failing.

Also we tried decreasing the min_free_kbytes=256, and with this also watermark is passed.

Our observation is that ZRAM/zsmalloc trying to allocate memory from CMA areas and failed.


Please let us know if anybody have come across the same problem and how to resolve this issue.





Thank You!
Regards,
Pintu